UT-Dallas scientist hopes tubes of earth tell dinosaurs' story

Inside a petrified forest in Arizona, a team of researchers gleefully awaits the arrival of several salami-shaped sections of rock.

John Geissman, a professor of geosciences at the University of Texas at Dallas, and his colleagues are drilling into Arizona’s Petrified Forest National Park to learn about a turbulent time in the Earth’s history. Between 235 million and 206 million years ago, during the Triassic era, the first dinosaurs evolved and an object from outer space smashed into the earth, disrupting life on the planet.

The team, which includes faculty from Columbia University and the University of Utah among others, hired a crew to drill 1,650 feet into the ground — deep enough to hold three Reunion Towers stacked on top of each other. As the rock cutters work, they extract long, cylindrical plugs known as core samples.

Each functions something like a reel of film, enabling scientists to rewind back through time and examine frozen snapshots of environmental changes. The sample also will allow researchers to more accurately date important events, like the possible meteorite strike and animal extinctions.

The $970,000 project, funded in part by the National Science Foundation, will probably keep Geissman and a rotating crew of colleagues working round the clock until mid-December, with a one-day break for Thanksgiving.

This Q&A with Geissman is part of The Dallas Morning News’ ongoing coverage of Dallas-based scientists and the effect of their research.

What did the Southwest look like during this time?

During this time period, river systems and lakes really dominated the show in an environment that was usually pretty warm. North America was poised close to the equator and was slowly moving north as the supercontinent Pangea broke up. It was a great place for big creatures to flourish.

What was happening with the dinosaurs?

This is the time period when the dinosaurs begin to evolve. What we’re dealing with is the evolution of relatively small early dinosaurs growing into larger and larger species.

What makes Arizona’s Petrified Forest a good location for this work?

It’s a relatively thick section of this age of sedimentary rocks that has been extensively studied on the surface and has provided a wealth of paleontological material demonstrating the evolution of dinosaurs. What’s also interesting about this sequence of rocks is that there is potential for the preservation of volcanic ash deposits, and these can be readily dated.

One component of volcanic ash isthe mineral zircon, which has a concentration of uranium. As you well know, uranium has unstable isotopes that decay with time, so we can use radioactive decay to provide very high-precision estimates as to the accurate age of the ash.

What is the benefit of drilling core samples to study this period?

There are a couple facets to this. One is that a core sample provides you with a spatially continuous record of a sequence of rocks. There is not a complete Triassic section of rock exposed in any one place. So, to study sequences of Triassic rocks, scientists traditionally go from place to place. By skipping around geographically, you miss things.

The other issue is that these materials on the Earth’s surface are exposed to processes like weatherization. The bottom line is we want fresh stuff that hasn’t been molded by exposure at the Earth’s surface.

What happens to the core samples once you’ve obtained them?

The first step is that each of the 5-foot-long segments of ours gets cut in half with a tile saw and capped with red and blue caps: blue goes on top, red goes on the bottom, so we know which way is up and down. All of these segments will be transported to the University of Texas at Austin to be CT-scanned to look for subtle variations in the deposits that might reflect cyclical changes in the Earth’s climate.

After that, it gets sliced right down the middle vertically. One half is archived at Rutgers University, which has a core storage repository, and the rest is then picked over for science and distributed among the project’s principal investigators.

What types of tests will you do on the cores in your lab at UTD?

What I’m going to be doing is preparing materials and specimens for measurement in our magnetometer to measure the magnetic pole of the core. This will help us date layers of the core sample more precisely.

We know very well that, going back maybe 300 million years, there were times when the earth was of normal polarity, like today, and times when it was of reverse polarity. The reversals are caused by some form of disruption in the interaction of the inner liquid core of our planet with the outer mantle.

The maximum duration for a reversal is no more than 10,000 years of earth time. That makes this a powerful and precise means of dating. Think of it as a zebra stripe code of one polarity over another in the rock record.

Can you talk more about the extinction event you hope to learn more about?

Yes. At the Petrified Forest National Park it’s represented by a very, very bizarre layer of a few centimeters where there is nothing but a mat of dead plant fragments. There’s a clear hiatus in the evolution of the dinosaurs, and a few species go extinct at this time.

Curiously, this is the exact same time as a major meteorite impact event in Quebec, Canada. It’s called the Manicouagan impact and is incredibly well preserved and well dated at about 215 million years in age.

The core sample will provide us with an opportunity to look at a continuous, well-preserved, unaltered sedimentary record through that time interval just like everything else we are coring. And we know there are at least several volcanic ash beds above and below the interval, so we can refine the age of that interval pretty nicely. We’ll also look at the chemistry of the sedimentary material and do a variety of different things that will help us better understand what took place at that time period.

How could a meteorite impact in Canada wipe out life in Arizona?

It’s a combination of things. It can send a wave of debris and initiate forest fires across a very, very large area. And at the same time it’s entirely possible that the debris that spreads out in the atmosphere may result in what we talked about a long time ago as a nuclear winter, which would freeze the Earth’s surface.

Is it similar to the extinction event that is thought to have wiped out the dinosaurs?

Absolutely, though likely it was on a smaller scale. If you Google the Manicouagan crater, there are great satellite images of it.

The bottom line is that if something responsible for a crater like the Manicouagan right now landed on the surface of our planet, it’s highly likely that the vast majority of the human race would be eliminated.

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